// Copyright (c) 2011 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef UI_VIEWS_WIDGET_DROP_HELPER_H_
#define UI_VIEWS_WIDGET_DROP_HELPER_H_

#include "base/macros.h"

namespace gfx {
class Point;
} // namespace gfx

namespace ui {
class OSExchangeData;
} // namespace ui
using ui::OSExchangeData;

namespace views {

class RootView;
class View;

// DropHelper provides support for managing the view a drop is going to occur
// at during dnd as well as sending the view the appropriate dnd methods.
// DropHelper is intended to be used by a class that interacts with the system
// drag and drop. The system class invokes OnDragOver as the mouse moves,
// then either OnDragExit or OnDrop when the drop is done.
class DropHelper {
public:
    explicit DropHelper(View* root_view);
    ~DropHelper();

    // Current view drop events are targeted at, may be NULL.
    View* target_view() const { return target_view_; }

    // Returns the RootView the DropHelper was created with.
    View* root_view() const { return root_view_; }

    // Resets the target_view_ to NULL if it equals view.
    //
    // This is invoked when a View is removed from the RootView to make sure
    // we don't target a view that was removed during dnd.
    void ResetTargetViewIfEquals(View* view);

    // Invoked when a the mouse is dragged over the root view during a drag and
    // drop operation. This method returns a bitmask of the types in DragDropTypes
    // for the target view. If no view wants the drop, DRAG_NONE is returned.
    int OnDragOver(const OSExchangeData& data,
        const gfx::Point& root_view_location,
        int drag_operation);

    // Invoked when a the mouse is dragged out of the root view during a drag and
    // drop operation.
    void OnDragExit();

    // Invoked when the user drops data on the root view during a drag and drop
    // operation. See OnDragOver for details on return type.
    //
    // NOTE: implementations must invoke OnDragOver before invoking this,
    // supplying the return value from OnDragOver as the drag_operation.
    int OnDrop(const OSExchangeData& data,
        const gfx::Point& root_view_location,
        int drag_operation);

    // Calculates the target view for a drop given the specified location in
    // the coordinate system of the rootview. This tries to avoid continually
    // querying CanDrop by returning target_view_ if the mouse is still over
    // target_view_.
    View* CalculateTargetView(const gfx::Point& root_view_location,
        const OSExchangeData& data,
        bool check_can_drop);

private:
    // Implementation of CalculateTargetView. If |deepest_view| is non-NULL it is
    // set to the deepest descendant of the RootView that contains the point
    // |root_view_location|
    View* CalculateTargetViewImpl(const gfx::Point& root_view_location,
        const OSExchangeData& data,
        bool check_can_drop,
        View** deepest_view);

    // Methods to send the appropriate drop notification to the targeted view.
    // These do nothing if the target view is NULL.
    void NotifyDragEntered(const OSExchangeData& data,
        const gfx::Point& root_view_location,
        int drag_operation);
    int NotifyDragOver(const OSExchangeData& data,
        const gfx::Point& root_view_location,
        int drag_operation);
    void NotifyDragExit();

    // RootView we were created for.
    View* root_view_;

    // View we're targeting events at.
    View* target_view_;

    // The deepest view under the current drop coordinate.
    View* deepest_view_;

    DISALLOW_COPY_AND_ASSIGN(DropHelper);
};

} // namespace views

#endif // UI_VIEWS_WIDGET_DROP_HELPER_H_
